U.S. patent number 6,859,186 [Application Number 10/357,296] was granted by the patent office on 2005-02-22 for flush-mounted antenna and transmission system.
This patent grant is currently assigned to Silver Spring Networks, Inc.. Invention is credited to Gary C. Lizalek, Juan R. Luglio.
United States Patent |
6,859,186 |
Lizalek , et al. |
February 22, 2005 |
Flush-mounted antenna and transmission system
Abstract
An apparatus mounted beneath or behind a surface and being
operable to transmit or receive wireless communication signals for
transmitting information from one location to a remote location.
The apparatus includes an antenna mounted substantially flush with
a surface. The apparatus also includes a communication device and a
matching network having a radial transmission line. The
communication device is connected to the antenna via the matching
network and includes either a transmitter, a receiver or a
transceiver.
Inventors: |
Lizalek; Gary C. (Oak Lawn,
IL), Luglio; Juan R. (Wauwatosa, WI) |
Assignee: |
Silver Spring Networks, Inc.
(Butler, WI)
|
Family
ID: |
32770989 |
Appl.
No.: |
10/357,296 |
Filed: |
February 3, 2003 |
Current U.S.
Class: |
343/767; 343/769;
343/789 |
Current CPC
Class: |
H01Q
1/286 (20130101); H01Q 13/18 (20130101); H01Q
13/10 (20130101) |
Current International
Class: |
H01Q
1/27 (20060101); H01Q 1/28 (20060101); H01Q
13/10 (20060101); H01Q 13/18 (20060101); H01Q
013/10 () |
Field of
Search: |
;343/769,789,767,771,700MS |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wong; Don
Assistant Examiner: Alemu; Ephrem
Attorney, Agent or Firm: Michael Best & Friedrich
LLP
Claims
What is claimed is:
1. An apparatus positioned beneath a surface, the apparatus
comprising: an antenna positioned substantially flush with the
surface, the antenna capable of either receiving radiation or
transmitting radiation when excited; a communication device coupled
to the antenna; and a matching network coupled to the antenna and
to the communication device, the matching network including a
radial transmission line, the matching network including a can
having a base and a sidewall, the base of the can and the sidewall
of the can defining a cavity, the matching network further
including a tuner element positioned within the cavity of the
can.
2. The apparatus as set forth in claim 1, wherein the antenna is an
annular slot antenna.
3. The apparatus as set forth in claim 1, wherein the matching
network further includes a connecting element coupling the matching
network to the communication device.
4. The apparatus as set forth in claim 1, wherein the matching
network further includes a post coupling the antenna to the tuner
element.
5. The apparatus as set forth in claim 4, wherein the radial
transmission line includes the tuner element and the base of the
can.
6. The apparatus as set forth in claim 4, wherein the can further
includes a diameter measured across the base and a height measured
along the sidewall, the diameter of the can being greater than the
height of the can.
7. The apparatus as set forth in claim 1, wherein the communication
device includes a transmission line and wherein the matching
network couples the antenna to the transmission line of the
communication device.
8. The apparatus as set forth in claim 1, wherein the matching
network has an equivalent electrical circuit including a radial
transmission line, a first capacitor, a second capacitor, and an
inductor.
9. The apparatus as set forth in claim 8, wherein the equivalent
electric circuit of the matching network further includes a series
shorted stub tuner.
10. The apparatus as set forth in claim 1, further comprising: the
can further includes a lip extending from the sidewall, the lip of
the can being included in the antenna; and a top plate having a
conducting portion and a non-conducting portion, the conducting
portion and the non-conducting portion being included in the
antenna.
11. The apparatus as set forth in claim 10, wherein the lip of the
can defines an annular shelf, and wherein a portion of the top
plate is positioned on the annular shelf.
12. The apparatus as set forth in claim 10, wherein the matching
network includes: a post coupling the top plate to the tuner
element.
13. The apparatus as set forth in claim 12, further comprising a
connecting element having a first conductor feed and a second
conductor feed, the first conductor feed electrically couples to
the tuner element, the post and the top plate, the second conductor
feed electrically couples to the can.
14. The apparatus as set forth in claim 13, wherein a transmission
line having a first conductor and a second conductor couples the
connecting element to the communication device.
15. The apparatus as set forth in claim 14, wherein the
transmission line has a first impedance and the antenna has a
second impedance, the first impedance being less than the second
impedance.
16. The apparatus as set forth in claim 15, wherein the first
impedance is approximately 50 ohms and the second impedance is
greater than approximately 200 ohms and the second impedance is
reactive.
17. The apparatus as set forth in claim 15, wherein the matching
network matches the first impedance to the second impedance.
18. The apparatus as set forth in claim 1, wherein the antenna has
an impedance greater than approximately 200 ohms.
19. The apparatus as set forth in claim 1, wherein the
communication device is a transmitter.
20. The apparatus as set forth in claim 1, wherein the
communication device is a receiver.
21. The apparatus as set forth in claim 1, wherein the
communication device is a transceiver.
22. An apparatus positioned substantially beneath a surface, the
apparatus comprising: an annular slot antenna positioned
substantially flush with the surface, the antenna capable of
transmitting radiation when excited; a can having a base and a
sidewall; a tuner element positioned within the can; a
communication device to excite the antenna; and a radial
transmission line coupling the communication device to the antenna,
the radial transmission line including the base of the can and the
tuner element.
23. The apparatus as set forth in claim 22, further comprising a
matching network coupling the communication device to the antenna,
the matching network including the radial transmission line.
24. The apparatus as set forth in claim 23, wherein the matching
network further includes a post coupling the antenna to the tuner
element.
25. The apparatus as set forth in claim 22, wherein the
communication device is a transceiver.
26. The apparatus as set forth in claim 22, further comprising: the
can further including a lip extending from the sidewall, the base
of the can and the sidewall of the can defining a cavity, the lip
of the can being included in the antenna; a top plate having a
conducting portion and a non-conducting portion, the conducting
portion and the non-conducting portion being included in the
antenna; the tuner element positioned within the cavity of the
can.
27. The apparatus as set forth in claim 26, wherein the lip of the
can defines an annular shelf, and wherein a portion of the top
plate is positioned on the annular shelf.
28. The apparatus as set forth in claim 23, further comprising: a
transmission line coupling the matching network to the
communication device, the transmission line having a first
impedance; and wherein the antenna has a second impedance, the
first impedance being less than the second impedance.
29. The apparatus as set forth in claim 28, wherein the matching
network matches the impedance of the transmission line to the
impedance of the antenna.
30. The apparatus as set forth in claim 28, wherein the first
impedance is approximately 50 ohms and the second impedance is
greater than approximately 200 ohms and the second impedance is
reactive.
31. The apparatus as set forth in claim 22, wherein the
communication device is a transmitter.
32. The apparatus as set forth in claim 22, wherein the
communication device is a receiver.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to antennas for effecting
wireless communication from an electronic device, and particularly,
to a flush-mounted antenna for the device.
There are many applications in which it is desired to obtain
information from a electronic device via wireless communication.
Often, the device is located beneath a surface of a supporting
structure, integrated into a surface of a supporting structure
and/or positioned within a housing or enclosure having an outer
surface. In order to effect wireless communication, the
communication signal much somehow be transmitted through the
surface. In the usual case, this is done by inserting an antenna
through a hole in the surface.
SUMMARY OF THE INVENTION
In some applications, however, it is desirable that the antenna not
extend outward from the surface, but rather be mounted flush with
the surface. Often, mounting the antenna flush with the surface
limits the area the antenna can occupy. Furthermore, mounting the
antenna flush with the surface may limit the ability of the device
to transmit and/or receive signals through the antenna. It
therefore becomes desirable, in these applications, to provide a
matching network for the device that will not significantly reduce
the total efficiency of the device during transmission and/or
reception and that can be configured in a small, compact
construction.
Accordingly, the invention provides an apparatus mounted beneath or
behind a surface and being operable to transmit or receive wireless
communication signals for transmitting information from one
location to a remote location. The apparatus includes an antenna
mounted substantially flush with a surface. In one embodiment, the
antenna is an annular slot antenna.
In another embodiment, the invention provides an apparatus for
transmitting and/or receiving wireless communication signals. The
apparatus is positioned beneath a surface and includes an antenna
positioned substantially flush with the surface. The apparatus also
includes a communication device and a matching network having a
radial transmission line. The communication device is connected to
the antenna via the matching network and includes either a
transmitter, a receiver or a transceiver.
In still another embodiment, the invention provides an apparatus
for transmitting and/or receiving wireless communication signals.
The apparatus is positioned beneath a surface and includes an
annular slot antenna positioned substantially flush with the
surface. The apparatus also includes a transmitter coupled to the
antenna via a radial transmission line.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a section view of an apparatus embodying the
invention.
FIG. 2 is an exploded view of the apparatus shown in FIG. 1.
FIG. 3 is a detailed view of the encircled portion of the apparatus
as shown in FIG. 1.
FIG. 4 is a perspective sectional view of another apparatus
embodying the invention with a portion of the apparatus broken
away.
FIG. 5 is an exploded view of the apparatus shown in FIG. 4 with
another portion of the apparatus broken away.
FIG. 6 is a schematic diagram illustrating a first electrical
circuit equivalent of the apparatus shown in FIG. 1.
FIG. 7 is a schematic diagram illustrating a second electrical
circuit equivalent of the apparatus shown in FIG. 1.
FIG. 8 is a schematic diagram illustrating an electrical circuit
equivalent of the apparatus shown in FIG. 4.
Before any embodiments of the invention are explained in detail, it
is to be understood that the invention is not limited in its
application to the details of construction and the arrangement of
components set forth in the following description or illustrated in
the drawings. The invention is capable of other embodiments and of
being practiced or of being carried out in various ways. Also, it
is to be understood that the phraseology and terminology used
herein is for the purpose of description and should not be regarded
as limiting. The use of "including," "comprising," or "having" and
variations thereof herein is meant to encompass the items listed
thereafter and equivalents thereof as well as additional items. The
terms "mounted," "connected," and "coupled" are used broadly and
encompass both direct and indirect mounting, connecting, and
coupling. Further, "connected" and "coupled" are not restricted to
physical or mechanical connections or couplings.
DETAILED DESCRIPTION
A first embodiment of an apparatus 20 in accordance with the
present invention is shown in FIGS. 1-3 and illustrated
schematically in FIGS. 6 and 7. The apparatus 20 is configured to
be positioned substantially beneath a surface 25 as shown in FIG.
1. In some constructions, the surface 25 is an outer surface of a
housing or enclosure that defines a cavity into which a
communication device, such as, for example, a transmitter, a
receiver and/or a transceiver (all not shown), is positioned. In
some constructions, the surface 25 is included in a support
structure or is a portion of a street, sidewalk or ground.
The apparatus 20 includes a top portion 30 which is positioned
substantially flush with the surface 25 and a bottom portion 35
which is positioned substantially beneath the surface 25. The top
portion 30 includes an antenna 40, which will be discussed below.
The bottom portion 35 includes a matching network 45 to couple the
antenna 40 to the communication device. In some constructions, the
matching network 45 couples the antenna 40 to a transmission line
(not shown), such as coaxial cable, which in turn couples to the
communication device.
Still referring to FIGS. 1-3, the apparatus 20 includes a can 50.
In the illustrated embodiment, the can 50 is substantially
cylindrical and includes a base 55 and a sidewall 60. As shown in
FIGS. 1 and 2, the diameter of the base 55 is substantially greater
than the height of the sidewall 60. In other constructions and in
other embodiments, the can 50 may have a different shape and/or
size than the can 50 illustrated in FIGS. 1-3. In some
constructions, the can 50 is formed from a conductive material or
metal. In other constructions, the can 50 is a plastic mold which
is plated with a conductive material or metal.
The sidewall 60 of the can 50 includes an inner surface 65 and an
outer surface 70. The base 55 of the can 50 includes a bottom
surface 75 and a top surface 80. The base 55 also defines an
aperture 85. The top surface 80 of the base 55 and the inner
surface 65 of the sidewall 60 partially define a cavity 90, i.e.,
the interior portion of the can 50.
The can 50 also includes an enlarged lip 95 extending from the top
of the sidewall 60. The lip 95 extends around the entire length of
the sidewall 60. A portion of the lip 95 is cut away forming an
annular shelf 100.
The apparatus 20 also includes a connecting element 110 which
extends through the aperture 85 in the base 55 of the can 50.
Transmission line, such as coaxial cable (not shown), connects to
the connecting element 110, as will be discussed below. The
connecting element 110 is a standard RF connector, such as a
threaded coaxial connector. In the illustrated embodiment, the
connecting element 110 is an SMA connector configured to receive
the coaxial cable transmission line. As illustrated in FIGS. 1 and
2, the connecting element 110 includes an inner conductor feed 115
positioned near the top of the connecting element 110 and extending
through the middle of the connecting element 110. In this
embodiment, the inner conductor feed 115 couples to the center
conductor of the coaxial cable when a connection between the cable
and the connecting element 110 is made.
The connecting element 110 also includes an outer conductor feed
120 substantially surrounding the inner conductor feed 115. The
outer conductor feed 120 couples to the outer conductor or shield
of the coaxial cable when a connection between the cable and the
connecting element 110 is made. The outer conductor feed 120 also
electrically couples to the base 55 of the can 50. The inner
conductor feed 115 is electrically isolated by the outer conductor
feed 120 by an insulator 125 formed from an insulating material,
such as, for example, plastic.
The apparatus 20 also includes a tuner element 140 positioned
within the cavity 90 of the can 50. In the illustrated embodiment,
the tuner element 140 is a round plate having a top side 145, a
bottom side 150, a sidewall 152 and an aperture 158. In other
constructions and in other embodiments, the tuner element 140 can
vary in shape and/or size without deviating from the spirit of the
invention. The tuner element 140 is positioned above the top
surface 80 of the base 55 of the can 50 by the connecting element
110 and forms a space 152 between the top surface 80 of the base 55
and the bottom side 150 of the tuner element 140. The inner
conductor feed 115 of the connecting element 110 extends through
the aperture 158 of the tuner element 140 and electrically couples
to the tuner element 140. During operation, the base 55 of the can
50 and the tuner element 140 form a radial transmission line 320
(shown schematically in FIGS. 6 and 7).
In some constructions, the tuner element 140 is a non-conductive
disc, such as a plastic disc, plated with a conductive material. As
illustrated in FIG. 2, the tuner element 140 is plated such that a
portion 155 of the top side 145 is plated with the conductive
material and a portion (not shown) of the bottom side 150 is plated
with the conductive material. In this construction, the tuner
element 140 also includes apertures 160. The sidewalls defining the
apertures 160 are also plated such that the plated portion 155 of
the top side 145 is electrically coupled to the plated portion of
the bottom side 150. As shown in FIG. 2, the plated portion 155 of
the top side 145 and the plated portion of the bottom side 150 do
not extend across the entire diameter of the tuner element 140.
Stated differently, there is a non-conductive annular region 156
between the tuner element 140 and the can 50 along the entire
periphery of the tuner element 140, and on both the top side 145
and the bottom side 150.
In other constructions, the tuner element 140 is a conductive disc.
As shown in FIG. 1, the tuner element 140 includes a conductive
disc 170 surrounded by a non-conductive ring or gap 175. In this
construction, the top side 145 and the bottom side 150 are
electrically coupled by the conductive disc 170.
The apparatus 20 also includes a conductive post 180 positioned on
top of the tuner element 140. The conductive post 180 is
electrically coupled to the inner conductor feed 115 of connecting
element 110 either directly or via the tuner element 140. In some
constructions, the conductive post 180 is a solid cylinder of
conductive material or metal. In other constructions, the
conductive post 180 is a hollow cylinder of conductive material. In
the embodiment illustrated in FIGS. 1 and 2, the conductive post
180 includes a conductive base 185 defining an aperture 188 and
coupling to a conductive sidewall 190. As shown in FIGS. 1 and 2,
the inner conductor feed 115 extends through the aperture 188 and
electrically couples to the conductive post 180. In other
constructions, the conductive post 180 is a plastic cylinder plated
with a conductive material.
The apparatus 20 also includes a top plate 200 positioned on top of
the post 180. As shown in FIG. 1, the top plate 200 is configured
to be positioned on the annular shelf 100 of the can 50. In some
constructions, the top plate 200 is mounted to the post 180. In
other constructions, the top plate 200 is mounted to the annular
shelf 100, and in further constructions, the top plate 200 is
mounted to both the annular shelf 100 and the post 180.
The top plate 200 includes a top side 205, a bottom side 210, a
sidewall 215 and apertures 218. As shown in FIGS. 1-3, the top
plate 200 is plated such that the top side 205 includes a first
conductive portion 220 and a first non-conductive portion 222, and
the bottom side 210 includes a second conductive portion 225 and a
second non-conductive portion 228. As shown in FIGS. 1 and 2, the
first conductive portion 220 is substantially circular. As shown in
FIG. 3, the first conductive portion 220 is electrically coupled to
the second conductive portion 225 by the conductive sidewalls 230
defining the apertures 218.
Referring to FIG. 1, the first conductive portion 220 and the first
non-conductive portion 222 of the top plate 200 and the lip 95 of
the can 50 form an annular slot antenna 40. In some constructions,
the annular slot antenna 40 radiates and/or receives signals at a
center frequency of approximately 900 MHz and is an
omni-directional antenna. The annular slot antenna 40 is positioned
substantially flush with the surface 25. The remainder of the can
50, the connecting element 110, the tuner element 140, the post 180
and the second conductive portion 225 of the top plate 200 form the
matching network 45. Furthermore, when the antenna 40 is radiating,
the can 50 serves as a reflector. During operation, a portion of
the radiation transmitted by the antenna 40 that is directed at the
can 50 is reflected by the conductive base 55 and conductive
sidewall 60 of the can 50.
FIG. 6 is a schematic diagram illustrating a first electrical
circuit equivalent for the matching network 45 and the antenna 40
included in the apparatus 20 illustrated in FIGS. 1-3. FIG. 7 is a
schematic diagram illustrating a second electrical circuit
equivalent for the matching network 45 and the antenna 40 included
in the apparatus 20 illustrated in FIGS. 1-3.
Referring to FIGS. 6 and 7, the matching network 45 can be
equivalent to both the first electrical circuit matching network
300 and the second electrical circuit matching network 305. Both
matching networks 300 and 305 include a conductor 310, whose
structural equivalent is the connecting element 110, and an
inductor 315, which represents the inductance of the inner
conductor feed 115.
The matching networks 300 and 305 also include a radial
transmission line 320, a first capacitor 325 and a second capacitor
330. The radial transmission line 320 is the electrical circuit
equivalent for the base 55 of the can 50 and the tuning element
140. The first capacitor 325 is the electrical circuit equivalent
for the capacitance produced between the tuning element 140 and the
sidewall 60 of the can 50. The second capacitor 330 is the
electrical circuit equivalent for the capacitance produced between
the second conductive portion 225 of the top plate 200 and the
sidewall 60 of the can 50.
The difference between the first matching network 300 and the
second matching network 305 is the electrical circuit equivalent
for the post 180. For the first matching network 300, the
electrical circuit equivalent for the post 180 is a second inductor
335 representing the inductance of the post 180. However, the post
180 may also be represented electrically by a low impedance
transmission line, such as the transmission line 340 included in
the second matching network 305.
The electrical circuit matching networks 300 and 305 and the
structural equivalent, matching network 45, are used to efficiently
match the impedance of the antenna 40 (shown schematically as
antenna 350) to the impedance of the coaxial cable transmission
line (not shown) coupling the apparatus 20 to the communication
device (not shown). Typically, coaxial cable has an impedance of
approximately 50 ohms. In most constructions, the annular slot
antenna 40 has a high and/or complex impedance, such as, for
example, an impedance greater than approximately 100 ohms and/or an
impedance having a large capacitive reactance. In the illustrated
embodiment, the annular slot antenna 40 has an impedance of
approximately 200 ohms to approximately 300 ohms and has a highly
capacitive reactance.
In the illustrated embodiment, the dimensions of the components
included in the matching network 45 are configured to efficiently
match the impedance of the antenna 40 to the impedance of the
coaxial cable transmission line (not shown). In the illustrated
embodiment, the cavity 90 defined by the can 50 has a height of
approximately 1-inch ("in") and a diameter of approximately
3.25-in. The sidewall 60 has a thickness of approximately 0.2-in.
The tuner element 140 has a diameter of approximately 3.25-in and a
thickness of approximately 0.2-in. The conductive portion 155 of
the tuner element 140 has a diameter of approximately 3.0-in. The
post 180 has a diameter of approximately 0.9-in and a height of
approximately 0.6-in. The top plate 200 has a diameter of
approximately 3.7-in. The sidewall 215 of the top plate 200 has a
height of approximately 0.2-in, and the first conductive portion
220 of the top plate 200 has a diameter of approximately
2.7-in.
Another embodiment of an apparatus 420 in accordance with the
present invention is shown in FIGS. 4 and 5 and illustrated
schematically in FIG. 8. Common elements have the same reference
number as shown in the drawings relating to the apparatus 20.
Similar to the apparatus 20 shown in FIGS. 1-3, the apparatus 420
includes a top portion 430 which is positioned substantially flush
with the surface 25 (shown in FIG. 1) and a bottom portion 435
which is positioned substantially beneath the surface 25. The top
portion 430 includes an antenna 440, and the bottom portion 435
includes a matching network 445 to couple the antenna 430 to the
communication device. In some constructions, the matching network
445 couples the antenna 440 to a transmission line (not shown),
such as coaxial cable, which in turn couples to the communication
device.
Referring to FIGS. 4 and 5, the apparatus 420 includes a can 450
similar to the can 50 shown in the first embodiment. As shown in
FIGS. 4 and 5, the can 450 is substantially cylindrical and is
formed from a conductive material, such as metal.
Similar to the can 50 shown in FIGS. 1 and 2, the can 450 includes
a base 455 and a sidewall 460. The sidewall 460 of the can 450
includes an inner surface 465 and an outer surface 470, and the
base 455 of the can 450 includes a bottom side or surface 475 and a
top side or surface 480. The base also defines an aperture 485. The
top surface 480 of the base 455 and the inner surface 465 of the
sidewall 460 partially define a cavity 490, i.e., the interior
portion of the can 450. The can 450 also includes an enlarged lip
495 extending from the top of the sidewall 460. The lip 495 extends
around the entire length of the sidewall 460. As shown in FIGS. 4
and 5, a portion of the lip 495 is cut away forming an annular
shelf 500.
In the illustrated embodiment, the connecting element 110 extends
through the aperture 485 of the can 450. Similar to the apparatus
20 in the first embodiment, the outer conductor feed 120 of the
connecting element 110 electrically couples to the can 450.
As illustrated in FIGS. 4 and 5, the apparatus 420 also includes a
tuning cup 540 as the tuner element. The tuning cup or tuner
element 540 includes an indented base 550 and a sidewall 555. The
sidewall 555 includes an inner surface 560, an outer surface 565
and a top surface 566. As shown in FIG. 4, the apparatus 420
includes a space 568 between the inner surface 465 of the sidewall
460 of the can 450 and the outer surface 565 of the sidewall 555 of
the tuner element 540. Also shown in FIG. 4, the apparatus 420
includes another space 569 between the base 550 of the tuner
element 540 and the top surface 480 of the can 450. During
operation, the base 455 of the can 450 and the tuner element 540
form a radial transmission line 720 (shown schematically in FIG.
8).
In the illustrated embodiment, the base 550 of the tuner element
540 includes a top surface 570, a bottom surface 572, a distal
perimeter 574, a proximal perimeter 575 and an aperture 576. As
shown in FIGS. 4 and 5, proximal perimeter 575 of the base 550 is
raised compared to the distal perimeter 574 of the base 550. The
result is that the height of the space 569 between the bottom
surface 572 of the tuner element 540 and the top surface 480 of the
can 450 is larger near the proximal perimeter 575 than near the
distal perimeter 574.
The apparatus 420 also includes a pogo pin 580 coupling a post 585
to the inner conductor feed 115 of the connecting element 110. As
shown in FIG. 4, the post 585 and the pogo pin 580 extend through
the aperture 576 of the tuner element 540 to electrically couple to
the inner conductor feed 115. Thus, the tuner element 540
electrically couples to the inner conductor feed 115 of the
connecting element 110 via the post 585 and the pogo pin 580.
Similar to the apparatus 20 in the first embodiment, the apparatus
420 includes a top plate 600 positioned on top of the post 585. As
shown in FIG. 4, the top plate 600 is configured to be positioned
on top of the post 585 and on top of the annular shelf 500 of the
can 450. In the illustrated embodiment, the top plate 600 defines
an aperture 602 to receive the post 585.
As shown in FIGS. 4 and 5, the top plate 600 includes a top side
605, a bottom side 606 and a sidewall 608. In the illustrated
embodiment, the top plate 600 is a non-conductive plate, such as a
plastic plate, and does not include a conductive portion positioned
on the top side 605 of the plate 600 (such as the first conductive
portion 220 as shown in FIGS. 1-3). Rather, the apparatus 420
includes a circular conductive plate 610 positioned on the bottom
side 606 of the top plate 600. In some constructions, the
conductive plate 610 is adhered to the bottom side 606 of the top
plate 600 with a conductive or non-conductive adhesive. In other
constructions, the conductive plate 610 defines an aperture 615 to
receive the post 585 and is positioned and held near the bottom
side 606 by the post 585. In further constructions, the conductive
plate 610 is plated onto the bottom side 606 of the top plate 600.
When the conductive plate 610 is positioned on the bottom side 606
of the top plate 600 and the apparatus 420 is assembled, the
conductive plate 610 defines a non-conductive portion 630 of the
top plate 600 which extends between the lip 495 of the can 450 and
the conductive plate 610.
Referring to FIG. 4, the conductive plate 610 and the
non-conductive portion 630 of the top plate 600 and the lip 495 of
the can 450 form an annular slot antenna 440. Similar to the
annular slot antenna 40 illustrated in FIGS. 1-3, the annular slot
antenna 440 is also an omni-directional antenna and radiates and/or
receives signals at a center frequency of approximately 900 MHz.
Also similar to the first embodiment illustrated in FIGS. 1-3, the
remainder of the can 450, the connecting element 110, the tuner
element 540, the post 585 and the pogo pin 580 form the matching
network 445. Furthermore, similar to the can 50 of the first
embodiment, the can 450 of the second embodiment serves as a
reflector when the antenna 440 is radiating. During operation, a
portion of the radiation transmitted by the antenna 440 that is
directed at the can 450 is reflected by the conductive base 455 and
conductive sidewall 460 of the can 450.
Referring to FIG. 8, the matching network 445 is equivalent to the
electrical circuit matching network 700. The matching network 700
includes a conductor 710, whose structural equivalent is the
connecting element 110, an inductor 715, which represents the
inductance of the inner conductor feed 115 and the pogo pin 585,
and a radial transmission line 720. The radial transmission line
720 is the electrical circuit equivalent for the base 455 of the
can 450 and the base 550 of the tuning element 540.
The matching network 700 also includes a first capacitor 730, a
second capacitor 740 and a series shorted stub tuner 745. The first
capacitor 730 is the electrical circuit equivalent for the
capacitance produced across the space 568. The second capacitor 740
is the electrical circuit equivalent for the capacitance produced
between the top surface 566 of the sidewall 555 of the tuner
element 540 and the conductive plate 610. The shorted stub tuner
745 is the electrical circuit equivalent of the coaxial
transmission line formed by the sidewall 555 of the tuner element
540 and the post 585.
Similar to the matching networks 300 and 305, the electrical
circuit matching network 700 and the structural equivalent,
matching network 445, is used to efficiently match the impedance of
the antenna 440 (shown schematically as antenna 750) to the
impedance of the coaxial cable transmission line (not shown)
coupling the apparatus 420 to the communication device (not shown).
As stated previously, coaxial cable typically has an impedance of
approximately 50 ohms. In most constructions, the annular slot
antennas 440 has a high and/or complex impedance, such as, for
example, an impedance greater than approximately 100 ohms and/or an
impedance having a large capacitive reactance. In both the first
embodiment and the second embodiment, the antennas 40 and 440 each
have an impedance of approximately 200 ohms to approximately 300
ohms and has a highly capacitive reactance.
As stated previously, the dimensions of the components included in
both matching networks 45 and 445 are configured to efficiently
match the impedance of the antennas 40 and 440 to the impedance of
the coaxial cable transmission lines (not shown). In the embodiment
shown in FIGS. 4 and 5, the cavity 490 defined by the can 450 has a
height of approximately 0.9-in and a diameter of approximately
2.3-in. The tuner element 540 has a diameter of approximately
2.1-in, and the sidewall 555 of the tuner element 540 has a height
of approximately 0.7-in. The post 585 has a diameter of
approximately 0.3-in and a height of approximately 0.55-in. The top
plate 600 has a diameter of approximately 2.75-in. The sidewall 608
of the top plate 600 has a height of approximately 0.125-in, and
the conductive plate 610 has a diameter of approximately 1.85-in.
In other constructions and in other embodiments, the dimensions of
the components included in the matching networks 45 and 445 are
greater than or less than the dimensions listed of the components
shown in FIGS. 1-5.
Thus, the invention provides, among other things, an apparatus for
transmitting and/or receiving wireless communication signals.
Various features of the invention are set forth in the following
claims.
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